This invention relates generally to a fluid bed processing, and, more particularly, to an agitation system for a fluid bed processing system.
Fluid bed processing systems and methods can be used in a variety of different applications. For example, fluid bed processing systems and methods can be used to dry wet particles for further processing or discharge. Fluid bed processing systems and methods can also be used to coat particles by building identifiable layers evenly over an identified core. Further, fluid bed processing systems and methods can be used to granulate particles into larger aggregates in which the original particles can still be identified in the aggregates.
In fluid bed processing systems and methods, particles to be processed are loaded into a container and are then fluidized into an expansion chamber. If the particles are going to be coated or granulated, a solution is sprayed onto the particles. With the solution, either layers are coated on the particles or the particles begin to aggregate together to form larger particles. Regardless of whether or not a solution is sprayed on to the particles, the particles dry as they descend down in the expansion chamber and then are blown back up. This up and down process continues until either the particles are dry and/or the desired coating or agglomeration has occurred. The particles are then discharged from the container.
One problematic area with prior systems is in the bed or bottom of the container where the particles to be fluidized are located. As air is blown into the bed of the product chamber to fluidize and mix these particles, large bubbles or pockets of air are often formed in the bed of particles. These bubbles or pockets disrupt the fluidization process so that particles in the bed of the container are not uniformly fluidized into the expansion chamber across the container. This non-uniformity in fluidization also disrupts heat transfer in the bed of the container so that heat is not be uniformly distributed throughout the bed of particles. This non-uniformity in fluidization may also cause temporary undesired agglomeration of the particles in the bed of the container. When these undesired agglomerations are eventually broken apart during processing an aesthetically displeasing condition know as xe2x80x9cbrown eyexe2x80x9d results. To minimize these problems, the batch size of particles which can be loaded into the container and the spray rate are often reduced, however this reduces the production capacity of the fluid bed processing system.
Effective systems and methods for overcoming these problems have not yet been developed. For example, simply installing a blade or propeller to rotate around the circumference of the bottom of the container to correct these fluidization problems will not work effectively. The weight of the particles on the propeller in the bed of the container would make it difficult to rotate the propeller around the container. As a result, the motor necessary to drive the propeller would be prohibitively large and expensive. Additionally, the ends of the propeller would be prone to jamming from the weight of the particles. The batch size of particles loaded into the container could be reduced, but this would reduce the production capacity of the fluid bed processing system.
A fluid bed processing system with an agitation system in accordance with one embodiment of the present invention includes a product chamber with an interior and a plurality of elongated structures. The elongated structures extend at least partially across the interior of the product chamber and are positioned in the product chamber where the particles are located. The apparatus also includes a system for engaging the elongated structures to agitate the particles in the product chamber.
A fluid bed processing system with an agitation system in accordance with another embodiment of the present invention includes a product chamber with an interior and a plurality of pipes. The pipes extend at least partially across the interior of the product chamber and are positioned in the product chamber where the particles are located. Each of the pipes has at least one outlet jet located in the product chamber. A first source of fluid is connected to each of the pipes to supply a first fluid to the pipes and out through the outlet jets to agitate the particles.
A fluid bed processing system with an agitation system in accordance with another embodiment of the present invention includes a product chamber with an interior and a plurality of interconnected shafts. The interconnected shafts extend at least partially across the interior of the product chamber and are positioned in the product chamber where the particles are located. A drive system is connected to oscillate the interconnected shafts in at least one direction.
A fluid bed processing system with an agitation system in accordance with another embodiment of the present invention includes a product chamber with an interior and at least one shaft. The shaft extends at least partially across the interior of the product chamber along a first axis, rotates about the first axis, and is positioned in the product chamber where the particles are located. A plurality of agitating bars extend out from the shaft. A drive system is connected to rotate the shaft about the first axis. The system may include a plurality of shafts which extend across the product chamber, each along its own axis and each rotating about its own axis.
A method of fluid bed processing of particles with an agitation system in accordance with another embodiment of the present invention includes a number of steps. First, the particles are loaded into a product chamber with a plurality of elongated structures extending across a bed of the product chamber. Once the particles are loaded in the product chamber, the particles are agitated with the elongated structures. At least a portion of the particles are also fluidized into an expansion chamber above the product chamber with a first fluid from a first fluid source. The fluidized particles may be sprayed with a second fluid from a second fluid source.
The present invention provides a number of advantages including the ability to minimize or prevent the formation of transient agglomerates in the product chamber before the particles are dried or formed into enlarged particles. As a result, the condition known as xe2x80x9cbrown eyexe2x80x9d can be minimized or eliminated.
Another advantage of the present invention is that the particles are continuously agitated across substantially the entire bed of the product chamber, instead of having no agitation or only periodic agitation of portions of the particles across the bed of the product chamber. As a result, the present invention provides more uniform fluidization across and heat transfer characteristics in the particles in the product chamber. With more uniform fluidization and better heat transfer, larger batch sizes of particles can be loaded into the product chamber and higher spray rates can be used which increases the production capacity for the fluid bed processing system.
Yet another advantage of the present invention is that the embodiment with an agitation system with pipes with outlet jets provides better control over the agitation because a separate source of fluid from the one used to fluidize the particles is used to supply fluid to the pipes to agitate the particles. As a result, characteristics, such as the rate of flow for the fluids and the temperature of the fluids, can be optimized for agitating the particles and also for fluidization of the particles.
Yet another advantage of the present invention is that the embodiment with an agitation system with at least one shaft which extends across at least a portion of a product chamber along a first axis and rotates about the first axis can be rotated much more easily and with less jams than, for example, a propeller located in the bottom of the product chamber whose rotational movement is restricted by the weight of the particles in the product chamber.